Composite polymers containing active hydrogen atoms, and in particular, composite polyols are of importance in that they can be used as starting materials in many chemical reactions. Composite polyols, for example, are valuable starting materials in the preparation of polyurethanes. Composite polyols also referred to in the art as polymer/polyols (J. of Cellular Plastics, March 1966, pp. 84-96) are valuable starting materials for products which will impart superior properties to urethane foams, in particular flexible foams. They are usually prepared by the in situ polymerization of a vinyl monomer in polyol base to give a dispersion of the vinyl polymeric portion in the liquid polyol. It is believed that the stability of the dispersion obtained is dependent on the specific monomer applied.
It is known from U.S. Pat. No. 4,104,236 that polymer/polyols can be prepared by polymerizing acrylonitrile or acrylonitrile/styrene mixtures in the presence of a polyoxypropylene polyol having a molecular weight of at least 1500. The polymerization is carried out using 2,2-azobisisobutyronitrile as the free-radical initiator. According to the disclosures in U.S. Pat. No. 4,210,727 polyol/graft polymer compositions can be obtained by polymerizing ethylenically unsaturated compounds (acrylonitrile or acrylonitrile/styrene mixtures) with a polyol in the presence of very specific peroxydicarboxylic acid-di-(polyol)esters as free-radical initiators. A disadvantage is, of course, that the radical initiators are not readily available and have to be prepared via a number of process steps in a rather cumbersome way.
Therefore, it would be of great interest to develop a process for the preparation of composite polyols which will lead to polyurethane foams which have improved load bearing properties, preferably with (near) retention of elasticity as measured by elongation at break and without increase in density, from easily accessible starting materials. In order to comply with the performance parameters as discussed hereinabove, the composite polyol should contain a blend of block copolymers and, optionally, homopolymers with polyol in the form of a fine dispersion giving the composite polyol good homogeneity and stability as well as an acceptable viscosity.